Despite the recommendation of the neurologist who assessed him after the 2006 incident, Henry was cleared to fly with no restrictions. Smith acknowledges that he, too, saw pilots who continued to suffer from the effects of their DCS episodes even after they were cleared. Kimbrough says he felt fine to fly, but was still a little surprised the Air Force sent him back up to high altitude only six months after his incident. “I only know they needed me,” he says.

A few months after he was cleared to fly, Henry had another brush with central nervous system DCS. At high altitude, he suddenly had the sensation of free-falling. Though completely awake, he slumped over in his seat, unable to move. He recovered and landed safely, but it quickly became clear that DCS had taken its toll on his brain. He was grounded permanently, and today has problems with short-term memory and reasoning.

In 2008, two years after Henry’s incidents, the increasing frequency and severity of DCS cases among U-2 pilots prompted Jersey and his colleagues to look through the Air Force’s medical records to see if they could find a pattern. As a new flight doctor at Beale, Jersey saw a DCS case his first week, and another soon after. He quickly realized that the Air Force had a serious problem. He and the other flight doctors, along with the squadron commander, went to Air Combat Command to request an investigation. A panel was formed to conduct a study and recommend what to do next.

Jersey points out that the study is based on military records alone, which are often inconsistent and can’t substitute for proper observation of the incidence of DCS. It is also possible that the increase in the DCS cases reported is partly due to a change in culture within the U-2 program: The stigma around admitting illness has faded, and the Air Force has loosened its rules about permanently grounding sick pilots. The committee on DCS feels confident, however, that the risk has increased, and that the U-2 program needs to change the way it does things.

Henry says he first really understood what had happened to him when his wife sent him a Federal Aviation Administration brochure on DCS she’d found on the Internet shortly after his first severe incident. He says that his training lacked much of the basic information in the circular. He also thinks the Air Force needs to protect pilots by addressing the tempo of operations.

“We all love doing what we do,” says Henry. “But I do think that it’s senior leadership’s job to be more conservative. It’s our job to push hard, as the warrior. And then senior leadership needs to be there to pull back and go, ‘Okay, appreciate the effort, but I want [you] to be safe.’ ” He also points out that there are only 33 U-2s in the Air Force fleet (NASA has two more), so the service can’t afford to crash any.

Smith is more forgiving of the U-2 program’s slowness to react. “I think the Air Force—as well as they understood the problem, as well as medical people could explain it to them—I think they tried to keep us safe,” he says. “It’s just, you know, things don’t move that quickly in the Air Force.”

The Air Force is now taking a number of steps to mitigate the risk to its U-2 pilots, partly as a result of Jersey’s study, according to Lieutenant Colonel Tadd Sholtis, deputy director of public affairs at Air Combat Command. The service is more thoroughly tracking DCS incidents, which will enable further studies to better isolate its causes. U-2 pilots are also performing enhanced pre-breathing, which includes exercise, a practice already common in the astronaut corps. Most important, plans are under way to modify the cockpit’s pressurization from the current 29,000-foot altitude equivalent to a much more comfortable 15,000-foot equivalent.

It will likely be several years before the Air Force knows whether the recent steps are helping. In the meantime, the war in Afghanistan continues to demand frequent, high-altitude flights by U-2 pilots.

For a few years it looked like the Air Force had an alternative to the U-2 that could render the DCS problem moot. The Northrop Grumman Global Hawk, an unmanned, remotely piloted drone, can fly almost as high, and do almost everything a U-2 can do. But this January the Pentagon announced it was cutting a variant of the Air Force’s Global Hawk program, Block 30, that had the same capabilities as the U-2 but was not sufficiently cheaper to fly and maintain. With their retrofitted cockpits, the U-2 should be ready for many years of service.